This invention relates to breast cancer examination by ultrasonic scanning techniques and, in particular, discloses a new method and apparatus for safe and efficient detection of this disease. Carcinoma of the breast is the major cause of death from cancer in women, taking the lives of about 27,000 women in the United States every year. While the five-year survival rate for breast cancer revealed by self-examination is 45-55%, the use of early detection methods can give survival rates in the range of 80-85%. Currently, a controversy exists in the medical community regarding the desirability of mammography as a screening procedure because it has been claimed that the diagnostic advantages of mammography may be outweighed by the risk of inducing cancer by the procedure itself. Thus there is a need for development of alternative methods of early cancer detection.
One of these alternative methods is ultrasonic scanning of the breast by pulse-echo technique. This method basically involves directing short pulses of high-frequency sound energy at the breast followed by the detection of reflected waves. Reflection of the waves occurs at boundaries between the media through which the waves travel. Thus, reflection occurs at the interfaces between skin and fat tissue, or between the skin and the surrounding external medium. The presence of a tumor within the breast establishes such boundaries and the tumor will therefore be detectable from the reflection of ultrasonic waves. When the reflected waves (echoes) are displayed on a conventional B-scope, an outline of the boundary of the tumor will appear on the display. Differentiation between solid and cystic masses may be obtained by a high gain setting in which case a solid mass will appear as a bright area whereas a cystic mass will appear as a dark (echo-free) area, because the fluid in the cyst is essentially transparent to acoustic energy.
Various ultrasonic scanning techniques are presently employed for breast cancer examination, but several drawbacks remain. In typical applications of this method, the woman being examined lies in a prone position with one breast immersed in a water bath and with the ultrasonic transducer scanning in a horizontal plane. Other techniques used require the patient to lie on her back during the test. These methods are cumbersome, and are not suited for mass screening. Also, the use of methods currently available often leads to deformation of the breast or to movement of the breast during scanning, resulting in inaccuracy and poor reproducibility.